1. Field of the Invention
The present invention relates to a portable device having an image pick-up unit and to an exposure adjusting device and, more specifically, it relates to a portable device having an image pick-up unit that adjusts brightness of an object (hereinafter referred to as exposure) utilizing an auxiliary light source, as well as to an exposure adjusting device.
2. Description of the Background Art
When an object is picked-up by a camera, exposure level is adjusted as described in Japanese Utility Model Laying-Open No. 58-83864. This laid-open application discloses a light adjusting device adjusting quantity of light emitted by an auxiliary light source for image pick-up. The light adjusting device receives light reflected from the object and adjusts the quantity of light emitted by the light source such that the exposure level detected from an image signal based on a photo reception signal attains to an appropriate level.
Japanese Patent Laying-Open No. 6-222429 discloses a strobe that automatically adjusts light emission of a flashing discharge tube. Specifically, in accordance with the diaphragm stop at the time of image pick-up, data representing quantity of strobe light emission corresponding to appropriate exposure is set, and the set data is input to one side of a comparator. To the other side of the comparator, data representing a result of integration of a current in accordance with the level of the reflected light from the object is input. When the data at the two inputs of the comparator match, emission of light from the flashing discharge tube is stopped.
Japanese Patent Laying-Open No. 2000-267151 discloses a camera that controls the quantity of stroboscopic light emission. According to this laid-open application, before a normal light emission by a strobe for image pick-up, a preliminary light emission of the strobe is performed to adjust exposure, and in accordance with the result of evaluation of the light reflected from the object at the time of the preliminary light emission, the level of the normal light emission of the strobe is determined.
Japanese Patent Laying-Open No. 2001-230970 discloses an apparatus that picks-up an image of an object in accordance with image pick-up conditions defined by the position of the object. Specifically, at the time of image pick-up, distance to the object is measured, for example, by a distance measuring sensor, and based on the measured distance, various conditions including the quantity of light emission by a strobe are determined.
The light adjusting device disclosed in Japanese Utility Model Laying-Open No. 58-83864 is fixedly provided in connection with a television camera fixedly installed at an entrance for picking-up an image of a visitor. Therefore, the quantity of light emission is adjusted simply to compensate for underexposure, while the distance between the light adjusting device and the object and the distance between the camera and the object do not vary. Therefore, it is impossible by the technique described in this reference to adjust the quantity of light emission while linearly following variation in the distance between the camera and the object.
According to Japanese Patent Laying-Open No. 2000-122128, quantity of light entering an imaging device is controlled by arranging an ND filter in front of the imaging device. By this arrangement, it becomes possible to effectively change the distance between the object and the imaging device, though the distance is actually kept constant, and in this manner, the quantity of strobe light emission is adjusted.
Japanese Patent Laying-Open No. 60-6930 discloses a method of controlling exposure of a camera. Specifically, exposure of a camera is adjusted by using data of a range that can be regarded as appropriate exposure of a film, data of film sensitivity and data of light intensity from an object.
As described above, none of the techniques disclosed in Japanese Patent Laying-Open Nos. 2000-122128, 60-6930 and Japanese Utility Model Laying-Open No. 58-83864 is capable of adjusting quantity of light emission while linearly following the change in distance between the camera and the object. Therefore, it is not possible to pick-up an image with optimal exposure level while linearly following the change in distance between the camera and the object.
According to Japanese Patent Laying-Open No. 6-222429, the quantity of strobe light emission is determined such that the optimal exposure is attained in accordance with the diaphragm stop at the time of image pick-up. Therefore, when the distance between the camera and the object happens to change as the camera moves, for example, the optimal exposure set in accordance with the diaphragm stop would result in under-exposure or over-exposure.
The technique disclosed in Japanese Patent Laying-Open No. 2000-267151 has a problem that, when the camera moves and the distance between the object and the camera changes between the preliminary light emission and the normal light emission, optimal exposure level would not be attained by the level of normal strobe light emission determined immediately before the movement.
According to Japanese Patent Laying-Open No. 2001-230970, image pick-up conditions including the quantity of light emission are determined based on the distance to the object detected by a distance measuring sensor. Therefore, the structure of the device becomes complicated by the incorporation of the sensor, and the cost of the device also increases.